Bring 3 cups water to a rolling boil in a medium saucepan. Stir in bulgur, immediately reduce heat to low, and then cover and simmer it until wheat is tender, about 15 minutes. Drain in a sieve with small holes and let cool for about 15 minutes.
Place cooked bulgur into a large, deep bowl. Add oil and toss well. Add diced plum tomatoes, tuna, sliced scallion, parsley, salt and pepper, then lightly toss. Divide salad greens among 4 plates and heap them along one side. Spoon tabbouleh salad along other side.